Hitherto, copolymers containing a unit derived from a polyfluoroalkyl group-containing polymerizable monomer are widely used as a water- and oil-repellent agent. In order to obtain the polyfluoroalkyl group-containing copolymer, a polymerization method such as a bulk polymerization, a solution polymerization, a suspension polymerization and an emulsion polymerization can be used. Generally, the solution polymerization and the emulsion polymerization are used. Among them, an aqueous emulsion prepared by the emulsion polymerization is advantageous over a solvent dispersion prepared by the solution polymerization, in view of a work-environmental problem and an effect on environment.
A textile treated with the water- and oil-repellent agent are widely used as, for example, usual clothes, sport clothes, interior goods, out door goods and medical non-woven fabrics. The improvement of properties such as softness, soil resistance and water resistance, and durability of the properties in addition to water- and oil-repellency is increasingly sought according to the spread of use.
Especially, it is desired that a non-woven fabric made of a thermoplastic resin (particularly a polyolefin resin such as polypropylene) exhibits high water repellency and hydrostatic resistance also at low-temperature treatment in view of heat resistance of the fabric.
For example, WO2002/064696, U.S. Pat. No. 5,344,903 and U.S. Pat. No. 4,100,340 disclose that a composition comprising a copolymer obtained from monomers such as a perfluoroalkyl group-containing acrylate and vinylidene chloride is used for the water- and oil-repellent treatment of non-woven fabrics.
Hitherto, a polyfluoroalkyl group contained in the polyfluoroalkyl group-containing polymerizable monomer used in the water and oil repellent composition for these applications is generally a perfluoroalkyl group having at least 8 carbon atoms.
Recent study results (EPA Report “PRELIMINARY RISK ASSESSMENT OF THE DEVELOPMENTAL TOXICITY ASSOCIATED WITH EXPOSURE TO PERFLUOROOCTANOIC ACID AND ITS SALTS” (http://www.epa.gov/opptintr/pfoa/pfoara.pdf)) and the like clarify that a PFOA (perfluorooctanoic acid) doubtfully has a potential risk of environmental load. EPA (Environmental Protection Agency of USA) announced on Apr. 14, 2003 that the EPA intensifies the scientific investigation on PFOA. On the other hand, Federal Register (FR Vol. 68, No. 73/Apr. 16, 2003 [FRL-2303-8]) (http://www.epa.gov/opptintr/pfoa/pfoafr.pdf),
EPA Environmental News for release Monday April, 2003 “EPA INTENSIFIES SCIENTIFIC INVESTIGATION OF A CHEMICAL PROCESSING AID” (http://www.epa.gov/opptintr/pfoa/pfoaprs.pdf), and
EPA OPPT FACT SHEET Apr. 14, 2003 (http://www.epa.gov/opptintr/pfoa/pfoafacts.pdf) announced that a long chain fluoroalkyl group (telomer) may possibly metabolize or decompose to PFOA.
Recently, the use of a polymerizable monomer containing a short-chain Rf group have been studied for the purpose of decreasing the load on environment.
For example, WO03/062521 discloses a water and oil repellent composition comprising a copolymer of a short-chain Rf group-containing (meth)acrylate and vinyl chloride (VCl) or vinylidene chloride (VdCl2) for the purpose of increasing the water resistance. This composition has insufficient water- and oil-repellency and water resistance and insufficient stability to long-term storage and contaminant.
In addition, WO02/083809 and WO04/035708 describe examples using a short-chain Rf group-containing polymerizable monomer, and agents described in these publications suffer from insufficient water- and oil-repellency and water resistance.
EP-1493761A1 describes that the decrease of molecular weight of the short-chain Rf group-containing (meth)acrylate copolymer can improve the performances. This copolymer has insufficient water repellency on particularly cotton fibers and cotton mixture fibers.
A document (Maekawa et al., a Preprint of 16th Fluorochemistry forum, page 25 (1991)) discloses that, in a polymer comprising a repeat unit derived from an Rf group-containing acrylate, a receding contact angle is decreased and water- and oil-repellency is deteriorated, if the chain length of the Rf group is decreased. The studies conducted by the present inventor also reveal that, in a polymer comprising a repeat unit derived from an Rf group-containing acrylate, if the chain length of the Rf group is simply decreased, the water- and oil-repellency is deteriorated and further a water leakage in a heavy rain durability test such as a Bundesmann test is remarkably increased (deterioration of water resistance).
As the methods of overcoming the above-mentioned problems, for example, WO2004/096939A1 discloses that an alpha-substituted acrylate copolymer comprising a short-chain Rf group has good water- and oil-repellency. In addition, WO2005/047416 illustrates examples comprising a copolymer of a short-chain Rf group-containing alpha-substituted acrylate and vinyl chloride and shows that said examples have good water- and oil-repellency.
A water- and oil-repellent agent, however, which is an aqueous dispersion composition comprising the short-chain Rf group-containing copolymer has not always exhibited satisfactory performances in applications requiring the treatment at a low temperature.
That is, the conventional arts do not have a water- and oil-repellent aqueous dispersion which is an alternative compound having chemical structure different from “telomer” and which have both object of decreasing environmental load and high water repellency, hydrostatic pressure resistance and low-temperature curing property.
An object of the present invention is to provide a composition which comprises an alternative compound having chemical structure different from “telomer” and which can impart high water repellency and hydrostatic pressure resistance to a textile substrate under a low-temperature curing conditions.
After intensively studying the causes of problems of conventional arts, the present inventor discovered that the alpha-substituted acrylate copolymer containing the short-chain Rf group has the tendency that the melt viscosity is higher in comparison with an unsubstituted acrylate copolymer, and that the former copolymer has the defects that the former copolymer has poor film formability at the low-temperature cure so that good performances are not easily exhibited.
WO2004/096939 and WO2005/047416 illustrate disclose various compounds which can be used as a comonomer contained in the short-chain Rf group-containing alpha-substituted acrylate copolymers. Conventionally, vinyl chloride (VCl) and vinylidene chloride (VdCl2) have been used in copolymers used in water- and oil repellent agents for the purpose of improving, for example, the adherence to fibers.
Hitherto, however, the study in view of copolymerizability between the short-chain Rf group-containing alpha-substituted acrylate and the comonomer nor the study on relevancy of water- and oil-repellency has not been made.